A Quick Mayonnaise Primer

• Mayonnaise's creamy texture and tang, so similar to sour cream, might easily create the impression that it's a dairy product. Nothing could be further from the truth. Mayonnaise is what's called an emulsified dressing, meaning its water-based ingredients -- the egg itself, as well as lemon juice or vinegar -- are combined in a stable mixture with vegetable oil. Oil and water proverbially don't mix, but egg yolks contain lecithin and other emulsifiers which bond to both water and fats. This keeps the two from separating the way they would in a vinaigrette. For bakers, this makes mayonnaise a quick fix for missing ingredients.

Mayonnaise for Oil

• Mayonnaise is mostly oil by volume, and you can use it as a direct substitute for the oil in many cake, cupcake, muffin or brownie recipes. Just measure out an equivalent quantity and stir it into your batter. This will increase the quantity of egg in your recipe slightly, but it's not usually enough to affect the outcome. The faint tang of the mayonnaise, provided by its vinegar or lemon juice, is more noticeable. The mayonnaise substitution works best in strongly flavored cakes such as spice cake, carrot cake or chocolate cake, which are sturdy enough to stand up to the vinegar flavor and incorporate it successfully into the overall taste of the cake.

Mayonnaise for Eggs

• Using mayonnaise as a substitute for eggs is a decades-old tradition, common during the Depression and widespread during the egg-rationing wartime years. Two tablespoons of mayonnaise is the usual substitute for each large egg called for in the recipe. It's not a direct equivalent, because the amount of egg in two tablespoons of mayonnaise is not substantial. Instead, the mayonnaise provides a similarly moistening and softening effect on the batter. It's more akin to other egg substitutions such as applesauce or flaxseed soaked in water, though the end result is richer and more flavorful.

Mayonnaise Alone

• In some recipes, and in boxed mixes, you can use mayonnaise as a replacement for both eggs and oil. Each egg is approximately 1/4 cup, so add that amount to the oil called for in your recipe and then substitute mayonnaise instead. Mayonnaise has a thicker texture, so you might also need to add a small amount of water or milk to thin the batter to the right consistency. Some bakers like to add mayonnaise as an additional ingredient in their cakes, rather than as a substitution. Like the pudding used by other bakers, this adds richness and moisture to the finished cake.